As the diagnostic radiologist moves from the analog world of film to the digital world, questions related to image resolution as well as the cost of the examination evolve. This is especially true in computer radiology and direct radiology, which are both beginning to replace plain film radiography. Should one replace analog film and what are the financial plus clinical ramifications? This round table tries to answer these questions, which will become ever more important as diagnostic radiology moves into the world of PACS.
Laurens V. Ackerman, MD, PhD
Director, Medical Informatics Department of Radiology
Rush-Presbyterian-St. Luke’s Medical Center
Round table participants include Leonard Berliner, MD, assistant director of radiology, Staten Island University Hospital, Staten Island, NY; H.K. (Bernie) Huang, DSc, professor, Department of Radiology, and director, Laboratory of Radiological Informatics, University of California, San Francisco; R. Gil Jost, MD, chief of diagnostic radiology, Mallinckrodt Institute, St Louis; and Carl Ravin, MD, professor and chairman of radiology, Duke University, Durham, NC. This round table was conducted electronically.
Axis Imaging News: How high is the quality of images acquired using digital radiography (DR) technologies?
Huang: The two types of DR technology approved by the US Food and Drug Administration (FDA) are the detector only and the complete imaging unit. The image quality of the former type depends on the x-ray unit to which it is attached and on the examination procedure. The latter type is a stand-alone unit that provides its own x-rays and patient bed apparatus. The image quality for this type of system is comparable to that for the film-screen detector system.
Berliner: For the DR system that we purchased, the image quality is excellent, compared with film. I am becoming convinced that the digital images are often better than conventional film. The system produces images that display an extraordinarily wide latitude, or grayscale, on a single exposure. This is most likely to be related to phenomena that are inherent in the digital process, as well as to the image reconstruction algorithms. As a result, images of the extremities show bone detail with great clarity, but can also display soft tissue structures clearly. You do not need a bright light in order to look for soft-tissue swelling or effusions.
For chest radiographs, there is no doubt that the images are uniformly better exposed, and they display a much wider grayscale than conventional film. Not only are common lung diseases such as pneumonia, atelectasis, and neoplasms well displayed, but the pulmonary interstitial structures are very well displayed. By comparison, conventional films almost appear burnt out.
Jost: Image quality with the DR systems is excellent. In spite of their inherently lower spatial resolution than film, the ability to distribute the grayscale information more appropriately leads to a significant improvement in contrast resolution. Hence, we particularly notice a superiority to film in areas of low contrast, such as the retrocardiac area or the abdomen. In our experience with a selenium-based system for chest radiography, our radiologists have uniformly preferred the digital image to that of our best film-screen systems. Further, our radiologists have determined that the soft-copy display of these images is comparable, and in some cases superior, to the digitally acquired film. In order to achieve this result, however, special care must be taken with the tonal and frequency characteristics of the display.
Ravin: DR encompasses a wide range of imaging technologies. The image quality of these various forms of digital imaging varies considerably. System performance can be best characterized by detective quantum efficiency (DQE). In general, however, most of the widely accepted DR techniques equal or exceed the capabilities of analog film.
Axis Imaging News: When might a digital mammography system gain FDA approval?
Berliner: There are more challenges to be met when dealing with digital mammography. Resolution of 2Kx2K is not sufficient for mammography. The whole field of mammography is, at this time, the most highly regulated area in radiology. Not only will digital mammography have to stand up to a side-by-side comparison with conventional film, strictly from an image-quality point of view, it will also have to conform to the standards and testing of the Mammography Quality Standards Act.
Digital mammography will not be universally accepted until it has been proven as effective as (if not more effective than) conventional mammography in detecting early breast cancer. Patients, referring physicians, and radiologists must feel confident that an early breast cancer would not be missed if digital mammography were employed, rather than conventional film. My gut feeling is that, ultimately, digital mammography will be better than conventional mammography because of its greater ability to display soft-tissue structures. Proving this, however, may not be an easy task.
Huang: According to a recent meeting on breast imaging and related topics organized by the US Office for Women’s Health and the National Cancer Institute and held in Washington, DC, in March 1999, representatives from the FDA still do not have a date for the approval of this technology — despite the urgings of both users and manufacturers that it is imperative for the FDA to take a bold step and approve it. My personal observation is that approval will take place at least another year from now. DR images should not be printed on film.
For 2K images in chest, abdominal, and skeletal regions, current picture archiving and communications systems (PACS) workstations would be sufficient. For 4K or higher digital mammography, however, a better workstation design and technology are required. Both federal agencies and manufacturers are aware of this issue. Progressive effort and funding are being seen in this area of research and development.
Jost: It is important for all of us to work together to prove to ourselves (and to the FDA) that full-field digital mammography systems are an important step forward. A key element in the development of useful, cost-effective digital mammography systems will be the development of an effective diagnostic workstation suitable for mammography. A key problem that has not yet been satisfactorily addressed is a suitable navigation scheme to allow efficient visualization of several very large images. With respect to image quality, I have little doubt that the soft-copy display of digital mammograms will prove to be quite acceptable. In fact, given the ability to enhance grayscale distribution found on a soft-copy monitor, the soft-copy presentation should be superior, particularly in the dense breast. It will be important to optimize the quality of the image presentation in order to avoid the need for window-level controls, which would slow down the diagnostic process. Digital mammography systems, if they are to be cost-effective, should speed up, not slow down, interpretation.
Axis Imaging News: What role will the cost of DR technologies play in their dissemination?
Jost: The cost of DR is a real problem. There is no way that we can expect additional reimbursement just because the acquisition modality costs more. In addition, the areas where DR can be justified are currently rather limited. Since most of the current systems are fixed in location, high patient volume in a single room is required. In areas where multiple examination rooms are located in a single area, computed radiography (CR) has significant advantages, because a single unit can serve each of the examining rooms. In addition, the cost of CR is dropping, and will probably continue to do so. The image quality of DR is certainly appealing — but, increasingly, cost (rather than quality) is an important element in a medical purchase decision. For these reasons, at these prices, the penetration of the market is likely to be slow.
Ravin: To the extent that the cost of digital technology exceeds that of analog film technology, introduction will be slowed; however, the technological advantages of digital technology (particularly the ability to communicate more effectively, as well as to store images more easily) will help drive implementation. In general, prices for digital technology have fallen as prices for support computer systems have decreased. I do not personally believe that additional reimbursement for DR is justifiable, although that approach has been taken in some countries, such as Japan.
Berliner: Cost will certainly play a major role in the dissemination of DR; those who are skeptical will delay the purchasing of digital equipment. Eventually, however, I believe that there will be universal acceptance of DR, and the price will ultimately be determined by the market. At this time, there is enough evidence that DR, if done properly, is cost-effective. By reducing film and processing costs, by increasing patient throughput, and by reducing the length of each examination, DR produces sufficient savings to achieve a return on investment within a reasonable amount of time.
This needs to be confirmed, and the information needs to be disseminated so that radiologists can get past the first hurdle in DR: the decision to go filmless. Once this hurdle is overcome, one can see how much DR really has to offer, including simultaneous availability of images throughout a wide network, increased availability of old studies, and future developments in digital image processing that may be able to elevate radiography to the level of CT and MRI, in terms of sophistication.
As far as additional reimbursement is concerned, I feel that reimbursements should cover the cost of the equipment. The radiology community, though, has to study and explore all of the potential benefits of DR to prove to patients and third-party payors that DR is an improvement over conventional film and is, therefore, worth additional expense. Additional reimbursement should not be the goal of DR, though; it is already cost-effective on its own.
Huang: Although both France and Japan provide incentives for health care providers to charge more if CR technology is used, this has not been a practice in the United States.
Axis Imaging News: Will radiation dose levels influence the adoption of DR?
Ravin: It certainly is possible potentially to reduce radiation exposure using DR, and we have done so in our environment. This is an additional advantage of the technology, but does not yet seem to be a major driver in its dissemination and implementation.
Berliner: If the radiation dose can be reduced by DR, it would help move more radiologists, patients, and consumer groups closer to DR. It is all a question of physics. I believe that, with a little research and development, several ways will be found to reduce patient exposure. Concerning consumer and environmental issues, I would add that DR helps reduce chemical waste products entering our environment.
Huang: My experience in using both prototype and FDA-approved DR systems demonstrates that the radiation dose delivered by these systems is equivalent to that of the conventional screen-film system.
Jost: There are opportunities to reduce radiation dose with DR because of its improved DQE. This is not likely to have much importance in the United States (except, perhaps, in some niche areas, such as pediatric radiology). There are other parts of the world, however, where radiation dose is more of a consideration. As DR systems begin to replace fluoroscopy applications, the radiation issue may become more important — if, in fact, we find that a reduced dose is achievable using these systems.
Axis Imaging News: What has been your service and maintenance experience for DR?
Jost: It is too soon to tell, but we have every reason to believe that DR systems will be stable, reliable, and easy to maintain. That does not necessarily mean that the costs of service and maintenance are likely to be reduced. It is attractive to think of eliminating the costs (and headaches) of maintaining a film-processing system in order to replace it with a digital acquisition system, but the costs of a maintenance contract (typically based on a percentage of the system’s purchase price) may be even higher than before.
Ravin: DR has functioned extremely well in our environment. We do have on-site engineering available, which clearly helps in keeping the equipment up and running. The upkeep does not seem to be significantly different from that required for analog film services.
Berliner: In my experience, DR is wearing quite well. Our system is an ingenious combining of tried-and-true technologies into a new concept and new product, but the underlying components are products with which we are all familiar: x-ray generators, x-ray tubes, motor-driven C-arms, computer workstations, anatomic programming, and charge-coupled device technology. The system is subject to the same wear and tear as any x-ray room, but, so far, downtime has been minimal. The service that we receive is excellent. I first heard about the manufacturer from its service organization, long before I ever met anyone from sales. It was apparent to me that the vendor understood the need to have a strong service organization before it placed units in the field.
Axis Imaging News: How does DR archiving affect your information storage needs?
Jost: Increased storage needs do not concern me. The cost of archiving a digital image is very small, and the costs are steadily decreasing. In addition, we have not taken full advantage of the opportunities for visually lossless data compression, and this could more than compensate for increased quantities of data. By the time DR is introduced on a broad scale, it is likely that storage costs will not be an important consideration.
Ravin: If one assumes that a PACS should hold all of the images generated in a radiology department, then DR provides a way to include traditional film-based studies. Even if one assumes that the PACS is intended only for direct digital technologies such as CT, MRI, nuclear medicine, and ultrasound, there are still going to be major increases in storage demand as these technologies improve. The number of images generated by CT has increased dramatically with the introduction of helical (and multislice helical) scanners. Clearly, additional images from CR and direct readout devices will generate more information, but the ultimate goal of PACS is to capture all images generated in the radiology department. Systems will have to be designed with this goal in mind.
Berliner: DR and PACS are two sides of the same coin. It makes no sense to have one without the other, and both are needed to bring health care into the 21st century. In order to meet the demands of patient care in a managed care environment, each hospital or health care facility needs to determine a plan for introducing not only DR and PACS, but also an entire electronic patient record and archiving system.
Huang: On the negative side, DR will require a much larger digital archive system than current PACS are providing. Digital linear tape and digital videodisc technologies are available, and their prices are affordable, compared with those of film archives. Current large-scale PACS have the built-in capacity to extend the archive system without affecting infrastructure. The positive aspect of this need is that the totally digital archive becomes a mandate, rather than an option — and the totally digital archive is a key to success for future health care delivery.
Axis Imaging News: Will DR promote the use of computer-aided diagnostic tools?
Berliner: Computer processing will open the door to new technological developments in conventional radiography. This may come in the form of image analysis, image augmentation, and image combination with other modalities. DR may, therefore, find a role in such areas as image-guided (or computer-aided) surgery in the not too distant future. I feel that radiologists will accept these new techniques if they provide meaningful additional information and if they can be accomplished easily.
Huang: This will eliminate the tedium and reduced quality of secondary image capture through a digitizer. Computer-aided diagnostic tools should be developed for use at both the image-acquisition device and the display workstation. During image acquisition, regions of interest with suspected abnormalities can be identified; during display, a thorough computer-aided diagnosis can be executed on those regions. These tools must be easy to use, must have high true-positive and low false-positive rates, must be fast, must be low in cost, and must be built into the digital imaging chain.
Jost: Computer-aided diagnostic tools, to be effective, must use the image in digital form, and DR is certainly one way to accomplish this. It is particularly relevant in digital mammography, an area where much of the computer-aided diagnosis work has been concentrated. There is no question that computers can help pinpoint problem areas in a medical image, but the challenge is to reduce the number of false positives so that the interpretation process is not slowed significantly.
Ravin: Clearly, one of the advantages of DR is the ability to bring to bear the power of computer-aided diagnosis (or computer-assisted detection). Such tools will have to be easy to use, with reasonably high sensitivity and specificity. If they are viewed as assisted detection, as opposed to assisted diagnosis, their introduction and acceptance will be faster.
Axis Imaging News: What impact on patient care and its delivery is DR likely to have?
Huang: DR will speed up the examination and diagnostic process. This translates into lower health care delivery costs.
Ravin: There is little question that diagnostic imaging will move toward DR as we go forward. Improved communication and, ultimately, the ability to provide any image, anytime, anywhere, will be major drivers of DR adoption, particularly in expanding health care systems. DR enables patients to be examined in environments closer (and more convenient) to them, but allows the most sophisticated diagnostic capabilities of central locations to be brought to bear in interpreting the resulting images. Information can be readily shared among multiple physicians across a health system and, indeed, between health systems.
Berliner: Ultimately, patients will derive the greatest benefits from DR. Routine radiography time can be reduced from 15 to 20 minutes per examination to just a few minutes. There are very few repeat exposures, there is no waiting for film processing, and the images are better and more uniformly exposed. While these factors are appreciated by ambulatory patients, they have a greater impact on trauma patients; sick, debilitated inpatients; pediatric patients; and any other patients who will benefit from decreased examination time and more rapid availability of images to the referring physician.
Jost: In specific instances, there are areas where the improved image quality that is achievable using DR will provide a more accurate diagnosis. On a broader scale, DR represents an important step along the road to putting all of the image information about a patient in digital form. When a PACS can be deployed at an enterprise level, there are opportunities to significantly change the way that radiology is practiced. Images can be interpreted by the proper specialist, leading to higher quality while allowing greater efficiency and, hence, lower costs.
Sabine Kremp is a contributing writer for Decisions in Axis Imaging News.